Cochlear implants and other inner ear prostheses are one option to help profoundly deaf or severely hearing impaired persons. Unlike conventional hearing aids that just apply an amplified and modified sound signal, a cochlear implant is based on direct electrical stimulation of the acoustic nerve. Typically, a cochlear implant stimulates neural structures in the inner ear electrically in such a way that hearing impressions most similar to normal hearing are obtained.
More particularly, a normal ear transmits sounds as shown in FIG. 1 through the outer ear 101 to the eardrum 102, which moves the bones of the middle ear 103, which in turn excites the cochlea 104. The cochlea 104 includes an upper channel known as the scala vestibuli 105 and a lower channel known as the scala tympani 106, which are connected by the cochlear duct 107. In response to received sounds transmitted by the middle ear 103, the fluid filled scala vestibuli 105 and scala tympani 106 function as a transducer to transmit waves to generate electric pulses that are transmitted to the cochlear nerve 113, and ultimately to the brain.
Some persons have partial or full loss of normal sensorineural hearing. Cochlear implant systems have been developed to overcome this by directly stimulating the user's cochlea 104. A typical cochlear prosthesis essentially includes two parts: the speech processor and the implanted stimulator 108. The speech processor (not shown in FIG. 1) typically includes a microphone, a power supply (batteries) for the overall system and a processor that is used to perform signal processing of the acoustic signal to extract the stimulation parameters. In state-of-the art prostheses, the speech processor is a behind-the-ear (BTE-) device. The implanted stimulator generates the stimulation patterns and conducts them to the nerve tissue by means of an electrode array 110 which usually is positioned in the scala tympani in the inner ear. The connection between speech processor and stimulator is usually established by means of a radio frequency (RF-) link. Note that via the RF-link both stimulation energy and stimulation information are conveyed. Typically, digital data transfer protocols employing bit rates of some hundreds of kBit/s are used.
One example of a standard stimulation strategy for cochlear implants is called “Continuous-Interleaved-Sampling strategy” (CIS), which was developed by B. Wilson (see, for example, Wilson B S, Finley C C, Lawson D T, Wolford R D, Eddington D K, Rabinowitz W M, “Better speech recognition with cochlear implants,” Nature, vol. 352, 236-238, July 1991, incorporated herein by reference in its entirety).
A problem associated with a cochlear prosthesis that includes an external speech processor and an implanted stimulator is the possibility of interchanging an external speech processor of one cochlear implant with that of another. For example, this may occur with young cochlear implant users at school. Since the settings of the cochlear implants of two different users are typically different, various problems may arise in the cochlear implant and/or with the user(s).